This invention relates to a method and a system for detecting fuel injection timing in a diesel engine, and more particularly to improvements in a method and a system for detecting fuel injection timing in a diesel engine, for use controlling fuel injection in a diesel engine having an electromagnetic spill type distribution fuel injection pump, wherein a member for converting rotary motion of a pump driving shaft into reciprocatory motion of a fuel pressure-feed plunger is provided, and the converting member is rotated relative to the driving shaft to vary a starting phase of a compression stroke of the fuel pressure-feed plunger, to thereby control the fuel injection timing.
In the past, electromagnetic spill type distribution fuel injection pumps have been used for precisely controlling the fuel injection quantity supplied to a diesel engine. In the electromagnetic spill type distribution fuel injection pump, a high pressure chamber defined by a forward end surface of a plunger and an inner wall surface of a cylinder is communicated with a low pressure chamber in a pump housing. An electromagnetic valve (referred to as an "electromagnetic spill valve") is provided for blocking and opening the path between the high and low pressure chambers. The electromagnetic spill valve is on-off operated to control the fuel injection quantity. More specifically, the communicating path is blocked by the electromagnetic spill valve before the plunger is lifted in a direction of reducing the volume of the high pressure chamber. When the plunger is lifted and a preset quantity of fuel has been injected, the communicating path is opened by the electromagnetic spill valve to stop the fuel injection.
Detection of the fuel injection timing in distribution type fuel injection pump of this type may be performed by methods proposed by the applicant in Japanese Utility Model Laid-Open (Kokai) No. 164224/1983 and Patent Laid-Open (Kokai) No. 192842/1984, for example.
As shown in FIG. 13, an injection timing detecting device of the distribution type fuel injection pump proposed in Utility Model Laid-Open (Kokai) No. 164224/1983, includes a rotor 42E having teeth disposed on the outer periphery thereof for emitting pulses. The rotor 42E has missing teeth corresponding in number to the number of engine cylinders. A pickup 8 (hereinafter referred to as a "CA pickup") for detecting a crank angle reference position based upon the approach of one of the missing teeth is provided near the outer periphery of the rotor 42E at the inner side of a pump housing 42M. A pickup 9 for detecting the start of fuel injection from the approach of the missing tooth is provided near the outer periphery of the rotor 42E on a roller ring 42H used to convert rotary motion of the pump driving shaft 42A into reciprocating motion of the fuel pressure-feed plunger 42G. Thus, an advance angle at the injection timing is detected on the basis of a phase difference between an output from the CA pickup 8 and the pickup 9 for detecting the start of injection.
In the distribution type fuel injection pump for a diesel engine, proposed in Patent Laid-Open (Kokai) No. 192842/1984, rotation of the rotor (42E) provided on the pump driving shaft (42A) of the fuel injection pump (42) is detected by a pickup (8) provided on the pump housing (42M) so as to detect a crank angle reference position. Thus, the fuel injection timing can be detected from the crank angle reference position and an output from a timer piston position detector for directly detecting the position of a timer piston (42J). Furthermore, in another arrangement, the provision of a pickup on the roller ring (42H) makes it possible to directly detect the relative rotational angle between the roller ring and the pump driving shaft.
In all of the above conventional arrangements the crank angle reference position sensor (hereinafter referred to as a "CA sensor") has been provided in the fuel injection pump 42. Thus, unless the fuel injection pump 42 is accurately mounted relative to a crank angle reference of the engine, the actual injection timing goes out of order. Moreover, in practice, it is extremely difficult to accurately assemble the fuel injection pump 42 relative to the engine crank angle reference. The assembling should be performed with the movement (or lift amount) of the pump plunger 42G being measured with a micrometer or the like, thus increasing costs.